Method of accelerating the set of a cement slurry in well cementing operations



United States Patent 1 Claims. (Cl. 166-25 This is a division of application Serial No. 215,091

filed August 6, 1962, now US. Patent No. 3,171,480. The present invention relates to a new and improved method of cementing wells and more particularly to a new and improved method of accelerating the set of a cement slurry in well cementing operations when temperatures are relatively low.

Cementing casing when well temperatures are below about 60 F. and/or surface formations are frozen presents a serious problem in well cementing operations. In performing such well cementing operations in cold weather, it is not unusual for a period of 3-7 days to be required in order for the cement to set sufficiently for drilling operations to be continued. Cement slurries containing a gypsum cement, calcium chloride as an accelerator or other chemical accelerators have been used in such circumstances with varying degrees of success. The chemicals and amounts used must be varied with the particular type of cement used as well as in accordance with temperatures and pressures.

In using chemical accelerators, however, considerable caution must be exercised in order to prevent a flash setting of the cement slurry. In addition to the use of chemicals, the cement is often preheated or warmed, the mixing water is heated, and in some instances the hole is warmed, all for the purpose of controlling setting time.

An ideal or optimum cement. slurry is one which remains sufliciently fluid for a length of time to be pumped or introduced into a desired area or location in the well, and which will set or harden reasonably soon after placement so that a minimum of waiting-on-cement time occurs. Lengthy WOC times enhance the cost of drilling operations and are therefore undesirable.

This period of time in which the cement slurry remains sufiiciently fluid to be pumpable under the particular well conditions of temperature and pressure is known as thickening time. The thickening time must, of course, be of such length that the desired amount 'of slurry is mixed and placed in the well. It is well known that temperature or heat hastens the hydration of the cement components and thus decreases the thickening time. It can therefore readily be seen that low well and surface temperatures will prolong the thickening time andif sufficiently low may prevent the cement from setting at all. g

Temperatures ranging from 80 F.120. F. have been found to be particularly ideal in arriving at desired thickening and WOC (waiting on cement) times with most cement slurries. These optimum temperatures do not prevail during winter months or in certain cold climates, and as ordinary cements will not generally set within a reasonable time at temperatures below 60. -F., something must be done.

It is therefore a primary object of the present invention to provide a new and improved method of cementing in cold climates wherein the cement slurry is externally heated to provide a desired setting time and waiting-on-cement time.

It is an important object of the present invention to provide a new'and improved method of accelerating the set of a cement slurry in well cementing operations which may be applied to all types of cementing jobs.

Another important object of the present invention is to provide a new and improved method of well cementing wherein heat is chemically generated and externally applied to a cement slurry for accelerating the set thereof.

Another object of the present invention is to provide a new and improved method of well cementing, wherein waiting-on-cement time is reduced by the chemical generationof heat inside the casing, thereby heating same and in turn heating the cement slurry in the well.

Still another object of the present invention is to provide a new and improved method of heating a cementing slurry in a well bore utilizing a material which would function as a non plugging perforating fluid when fracturing or cleaning up the formation around the well bore.

Other objects and advantages of the presentinvention will be readily apparent from the description hereinbelow.

In carrying out the method of this invention, a well cementing operation is performed in a manner well known in the art. After the cement is mixed and displaced to the desired area in the well bore, a solution or liquid is placed behind the top plug. This liquid is heated a predetermined amount by the reaction of certain metals therewith and heats the casing in the well bore and consequently the cementing column and the formation. Although heat up to 1000" F. or more can be generated in this manner, it is preferred that the amount of heat generated be sufiicient to raise the temperatu're around the cementing column to a temperature of from about 80 F.-120 F. Other desired temperatures may be achieved without departing from the scope of the invention.

There are a number of ways of chemically generating heat and heat producing chemicals which may be used in the present invention. The heat generating operation should be one which has no deleterious effects on the well casing.

'Some of these methods are the addition of magnesium pellets, bars or pdwders to an aqueous acid solution and the addition of metallic sodium to water.

In addition to the heat generating solutions or methods set forth, above, it can be appreciated that there are others which can be used without departing from the scope of the invention.

Magnesium pellets (20-40 mesh) and hydrochloric acid are the preferred materials used as the heat gencrating solution. When acid reacts upon magnesium, a large quantity of heat is liberated in a very short time (8400 B.t.u./-lb of reacted magnesium).

There should be no casing damage from the use of the acid. The magnesium chloride formed bythe action of hydrochloric acid on magnesium is not harmful to the casing, nor will precipitation of magnesium hydroxide take place until the pH reaches 9. This will not 'occur in jspent acid.

The quantity of magnesium and acid to use will have to be determined by the particular set of circumstances "3 :9 involved. The desired amount of heat should be the governing factor on the quantity of magnesium.

Some data on the magnesium-hydrochloric acid system is set forth in Table I below:

Table ].-Dam on Jllg-HCI system Bulk density of magnesium 8.5 lbs/gal. or

63.4 lbs./ft. Absolute density of magnesium 1.74. 10

gals. of HCl 520 F.

By heating the inside of casing, it is possible to greatly improve the early strength of cement. For example, the compressive strength of API Class A Cement when cured for 6 hours at 120 F. is 905 p.s.i., while the same cement cured at 60 F. for the same length of time will not be set. After six hours at 120 F. a -50 Pozmix A Cement without bentonite has a compressive strength of 455 p.s.i., while the same cement will not be set at F. or 80 F. in the same time period.

The hydraulic cement mixes with which this invention may be employed to advantage include those in which any iydraulic cement of the character of Portland cement is the principal cementitious composition, pozzolanic cements or other cements used in well cementing operations. Any of the common aggregates and fillers may be employed in various proportions to meet diiferent structural requirements. These include stone, gravel, slag, sand, pozzolanic materials, fly-ash, and the like, and such specialized materials as metallic aggregates, aluminum powder, etc. The invention is also applicable to neat cement mixes containing no aggregate or filler. All such mixes are comprehended by the term hydraulic cement mix.

As indicated above, the invention does not preclude the use of other additives, as well as aggregates and fillers, for modifying various characteristics of the mixes for special purposes. For example, air entraining agents, cement dispersing agents, retarders, friction reducers, low fluid loss additives, accelerators, pigments, water-repellant compounds and other additives which may be employed in well cementing operations may also be used without departing from the scope of the invention.

Broadly, the present invention relates to a new and improved method of cementing wells at relatively low temperatures, wherein the cement slurry is pumped or placed in the desired location in the well, and thereafter the well casing or pipe is heated by the reaction of certain metals in aqueous solution displaced therein and thus the cementing column and formation.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials used, as well as in the details of the procedure and method and particular order of steps may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed:

l. A method of cementing wells under relatively cold climatic conditions, comprising the steps of:

(a) introducing a hydraulic cement slurry into a desired area in a well bore for cementing a well casing therein; and

(b) chemically generating heat inside the well chasing by injecting an aqueous solution thereinto and subsequently injecting into the aqueous solution a quantity of a metal reactive with said aqueous solution, which metal reacts with said aqueous solution and generates a sufiicient amount of heat to heat the well casing, wherein the amount of said metal and the amount of said aqueous solution are such that the reaction thereof and the reaction product formed thereby have substantially no deleterious effect on the well casing, thereby heating the cement slurry and accelerating the set thereof. 2. A method of cementing wells under relatively cold climatic conditions, comprising the steps of:

(a) introducing a hydraulic cement slurry into a desired area in a well bore for cementing a well casing therein;

(b) placing a cementing plug on top of the cement slurry;

(c) introducing a suificient quantity of an aqueous solution into the casing to cover the area desired to be heated; and,

(d) placing a predetermined amount of a metal reactive with said aqueous solution, in said aqueous solution, whereby the reaction of the metal with the aqueous solution generates a sutficient amount of heat to heat the casing, wherein the amount of said metal and the amount of said aqueous solution are such that the reaction thereof and the reaction product formed thereby have substantially no deleterious effect on the well casing, and thereby heating the cement slurry to accelerate the set thereof.

3. A method of cementing wells under relatively cold climatic conditions, comprising the steps of:

(at) introducing a hydraulic cement slurry into a desired area in a well bore for cementing a well casing therein;

(b) placing a cementing plug on top of the cement slurry;

(c) introducing a sufficient quantity of an aqueous acid solution into the well casing to cover the area desired to be heated; and,

(d) placing a quantity of magnesium in the form selected from the group consisting of pellets, bars, and powders, into the aqueous acid solution thereby generating a quantity of heat, heating the casing, wherein the amount of said magnesium and the amount of said acid solution are such that the reaction thereof and the reaction product formed thereby have substantially no deleterious effect on the casing, whereby the cement slurry is heated and the set thereof is accelerated.

4. The method of claim 3, wherein the aqueous acid solution is prepared from hydrochloric acid and a quantity of said acid and magnesium is used whereby the acid is completely spent upon reaction with the magnesium and the casing is left unharmed.

5. A method of cementing wells under relatively cold climatic conditions, comprising the steps of:

(a) introducing a hydraulic cement slurry into a desired area in a well bore for cementing a well casing therein;

(b) chemically generating heat inside the well casing by injecting an aqueous acid solution thereinto and subsequently injecting into the acid solution a quantity of magnesium metal which reacts with the acid solution and generates a sufiicient amount of heat to heat the well casing, wherein the amount of said magnesium and the amount of said aqueous acid solution are such that the reaction thereof and the reaction product formed thereby have substantially no deleterious eifect on the casing, thereby heating the cement slurry and accelerating the set thereof.

6. A method of cementing wells under relatively cold climatic conditions, comprising the steps of:

(a) introducing a hydraulic cement slurry into a desired area in a well bore for cementing a well casing therein;

(b) placing a cementing plug on top of the cement amount of heat to heat the well casing, wherein slurry; the amount of said metallic sodium and the amount (c) introducing a sufiicient quantity of water into the of said water is such that the reaction thereof and casing to cover the area desired to be heated; and, the reaction product formed thereby have substan- (d) placing a predetermined amount of metallic so- 5 tially no deleterious efiect on the well casing, thereby diurn in said water whereby the reaction of the heating the cement slurry and accelerating the set metallic sodium with the Water generates a sufiicient thereof.

amount of heat to heat the casing wherein the amount of said metallic sodium and the amount of said Water References flied y the Examinfli is tfhat tlzle tllrfa-cionhthereofbatndttlie reactisn 10 UNITED STATES PATENTS pro uc orme ere y ave su s an 1a y no eleterious efiect on the well casing, and thereby heat- 2217708 10/40 Scaramuccl 166*25 X ing the cement slurry to accelerate the set thereof. 2672201 3/54 Lorenz 166 38 X 7. A method of cementing wells under relatively cold 2872982 2/59 Wade 166 38 climatic conditions, comprising the steps of: 15 2975334 West et 16638 X (a) introducing a hydraulic cement slurry into a de- 166*25 slilredarea in a well bore for cementing a well casing OTHER REFERENCES erem;

Gatlin: Petroleum Engineering, Drilling and Well by injecting Water thereinto and Subsequently 20 Completions, Prentice-Hall, Inc., Englewood Clnfs,N.I.,

jecting into the Water a quantity of metallic sodium 1960 page 173 relied which reacts with the water and generates a sufficient BENJAMIN HERSH, Primary Examiner.

(b) chemically generating heat inside the well casing 

1. A METHOD OF CEMENTING WELLS UNDER RELATIVELY COLD CLIMATIC CONDITIONS, COMPRISING THE STEPS OF: (A) INTRODUCING A HYDRAULIC CEMENT SLURRY INTO A DESIRED AREA IN A WELL BORE FOR CEMENTING A WELL CASING THEREIN; AND (B) CHEMICALY GENERATING HEAT INSIDE THE WELL CHASING BY INJECTING AN AQUEOUS SOLUTION THEREINTO AND SUBSEQUENTLY INJECTING INTO THE AQUEOUS SOLUTION A QUANTITY OF A METAL REATIVE WITH SAID AQUEOUS SOLUTION, WHICH METAL REACTS WITH SAID AQUEOUS SOLUTION AND GENERATES A SUFFICIENT AMOUNT OF HEAT TO HEAT THE WELL CASING, WHEREIN THE AMOUNT OF SAID METAL AND THE AMOUNT OF SAID AQUEOUS SOLUTION ARE SUCH THAT THE REACTION THEREOF AND THE REACTION PRODUCT FORMED THEREBY HAVE SUBSTANTIALLY NO DELETERIOUS EFFECT ON THE WELL CASING, THEREBY HEATING THE CEMENT SLURRY AND ACCELERATING THE SET THEREOF. 